During helicopter missions requiring precise arrival at a specified location, time and fuel management can be one of the pilot's most attention demanding tasks, especially during high pilot workload flight operations or when such missions are flown in single pilot aircraft. In addition, mission requirements may involve a greater percentage of high pilot workload flight operations such as Nap of the Earth "NOE", adverse weather, and/or night flying. NOE flight operations involve varying airspeed and altitude in order to fly as close to the earth's surface as vegetation, obstacle, and light conditions will allow. NOE flight is used to limit exposure to threat weapons systems and to increase survivability, and requires almost constant pilot head-up and eye out the window attention to maintain ground and obstacle clearance. Additionally, the flying pilot must keep hands on the flight controls the majority of the time as adjustments to the flight path occur continuously.
In a two pilot aircraft, one pilot scans the world outside the cockpit while the other cross checks the instrument displays to monitor the aircraft while navigating. Any requirements to shift the flying pilot's visual attention inside the cockpit or move the pilot's hands from the grips at these altitudes significantly increases pilot workload and the risk of the mission.
While the tasks of computing remaining time and fuel are often given a lower priority than terrain and obstacle avoidance, errors in computing those parameters may result in serious consequences. Frequently during a mission the pilot needs to know whether the current rate of speed will mean an early or late arrival at a specified location, and whether fuel is being consumed faster than had been anticipated. These calculations must accommodate changes in speed due to terrain, threats, or weather, and must be constantly adjusted. On a typical mission the pilot periodically checks the current values of each of these parameters and compares them to the values obtained when the flight plan was last updated. Discrepancies between actual and planned time and fuel values can be compensated for by either altering the aircraft speed (within limits) or by changing the planned course or arrival time to accommodate the actual values. Errors in arrival timing can result in an unplanned encounter with the enemy or with friendly artillery, or a missed fuel rendezvous. Discrepancies in fuel consumption may indicate flight at speeds or in conditions other than those planned. Additionally, excess fuel consumption could indicate a possible aircraft fault affecting fuel flow and consumption. Insufficient fuel reserves can result in an aborted mission or the loss of the aircraft. Fuel management calculations require a high degree of mental effort, and can divert the pilot's attention away from higher priority tasks such as terrain and threat avoidance.